cluster: fix example topology url 404

[srstack]

What problem does this PR solve?

close #1839

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• nexustar

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[codecov-commenter]

Codecov Report

Merging #1840 (480710b) into master (bdc10b9) will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1840      +/-   ##
==========================================
- Coverage   53.01%   52.96%   -0.05%     
==========================================
  Files         303      303              
  Lines       34682    34682              
==========================================
- Hits        18385    18369      -16     
- Misses      14148    14159      +11     
- Partials     2149     2154       +5     

Flag	Coverage Δ
dm	24.73% <ø> (-0.06%)	⬇️
playground	12.64% <ø> (+<0.01%)	⬆️
tiup	14.39% <ø> (ø)
unittest	21.31% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/cluster/api/dmapi.go	59.88% <0.00%> (-4.07%)	⬇️
pkg/cluster/task/update_meta.go	84.95% <0.00%> (-2.15%)	⬇️
pkg/cluster/operation/destroy.go	59.45% <0.00%> (-0.64%)	⬇️
pkg/cluster/api/binlog.go	36.08% <0.00%> (-0.63%)	⬇️
components/dm/spec/topology_dm.go	84.31% <0.00%> (-0.57%)	⬇️

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[nexustar]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: b2debdf